Shielding system



2 SheetS -Sheet l Inventor: Albert vv. HUI 1,

JOB HIS Attorney.

A. W. HULL SHIELDING SYSTEM Filed Feb. 8, 1927 Fig.2.

m m a m n I I I m n m m n I r u 1 I n n n a I u I u I n m Feb. 18, 1930.

Feb. 18, 1930. w L 1,747,938

SHIELDING SYSTEM Filed Feb. 8, 1927 2 SheetsSheet 2 Fig. 5.

Inventor: Albert W. HUI I,

His Attovne g.

Patented Feb. 18, 1930 UNITED STATES PATENT OFFICE GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK SHIELDIN G SYSTEM Application filed February 8, 1927. Serial No. 166,778.

My invention relates to shielding systems for neutralizin the electrical coupling which tends to exist etween the input and output circuits of a space discharge device, and has for its principal object the provision of an improved apparatus whereby both internal and external feed-back between the input and output circuits of such a device are prevented.

It is known that internal feed-back between the output and input circuits of a space discharge device may be largely avoided by means of an extra grid interposed between the anode and control grid of the device and maintained at a constant potential with respect to the ground. This extra grid, however, is inefiective to neutralize the electrical coupling between the input and output circuit connections through which the currents of the device are transmitted. In accordance with my invention, external feed-back between the circuits of a shielded-grid device is avoided by the provision of an improved arrangement of the device and its circuits.

My invention will be better understood from the following description when considered in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referring to the drawings, Fig. 1 illustrates an amplifying system wherein my invention has been embodied; and Figs. 2 to 5 show modified embodiments of my invention.

Fig. 1 illustrates an amplifying system comprising a pair of shielded grid tubes 1 and 2 which are respectively provided with cathodes 3 and 4, with anodes 5 and 6, with control grids 7 and 8, and with screen grids 9 and 10. Heating current is supplied to the cathodes 3 and 4 through a circuit 11 which is grounded at one side to the shields 12 and 13. It will be observed that the cathode 3 and anode 5 are connected between a circuit 14 and ground through a circuit comprising a tuned circuit device 15 and a reactor 16; that the screen grid 9 is connected to a. circuit 17 through a reactor 18; and that condensers 19, 20 and 21, which are grounded through the same conductor as the cathode 3, are arranged to cooperate with the reactors or impedances 16 and 18 in keeping the high frequency currents out of the and 17.

In order to minimize circulating currents in the walls of the shields 12 and 13, it is desirable that the grounded terminals of the filter condensers 19, 20 and 21 be connected to the shield 12 through a single or common terminal, and that the filter condensers associated with the device 2 be likewise connected to the shield 13. Coupling between the output circuit of the device 1 and the input circuit of the device 2 is efi'ected by means of a coupling condenser 22, a resistance 23 being arranged to maintain the potential of the grid 8 at the average value required for proper operation of the device 2.

It has been found satisfactory to make the shields 12 and 13 in the form of tinned sheet iron boxes placed adjacent one another and each arranged to enclose the output and screen grid circuit connections of one device, the input circuit connections of another device, and the connections through which these output and input circuits are coupled together. Under these conditions, the input and output circuits of each device are completely shielded from one another and external feed-back greatly reduced or altoge'ther avoided. As previously indicated, internal feedback due to the capacity coupling between the control grid and the anode of the space discharge device is prevented by the screen grid.

A suitable arrangement of the screen grid with respect to the cathode and anode is described in a paper by Albert W. Hull and N. H. \Villiams entitled Characteristics of shielded-grid pliotrons and published in the Physical Review, pp. 432 138, vol. 27, No. 4, April, 1926. In this arrangement, an extra grid interposed between the control grid and anode is maintained at a constant potential and a grounded metal cylinder is fitted closely over the evacuated vessel. In order to facilitate neutralization of the coupling which tends to exist between the input and output circuits of the device, the lead to the control grid is taken out at the top of the de vice and the remainder of the leads are taken out at the bottom of the device.

power supply circuits 11, 14

The screens between the input and output circuits of the space discharge devices may arranged in various ways.

Fig. 2 shows an arrangement wherein the circuits to be screened from one another are enclosed in a series of cells or compartments formed by a receptacle 30and a ser1es of partitions 31 and 32 adapted'to be sli d into the receptacle 30 and fixed in the1r illustrated positions in any suitable manner such as by v soldering, welding or the like.

Fig. 3 shows a receptacle 33 provided with a plurality of diagonal partitions 34 and 35 which receive the upper ends of the devices, and form compartments whereby the input and output circuit connections of each device are screened from one another. It will be apparent that this arrangement'permits any one of the devices to be removed without disturbing the connections of the other device or devices.

Fig: 4 shows an arrangement wherein the condenser and reactor of the tuned circuit 15 are respectively enclosed in receptacles 36 and 37 which are grounded at 38 and practically neutralize the coupling which tends to exist between the input and output circuit connections of the devicel. This form of screen has the marked advantage that it is much simpler and less expensive than those illustrated by Figs. 1 to 3.

Fig. 5 shows a more elaborate arrangement comprising a receptacle 39 divided into compartments 40 and 41 which respectively enclose the input circuit connections of the devices 1 and 2 and into compartments 42 and 43 which respectively enclose the output circuitconnections of the devices 1 and 2. It will be apparent that this arrangement permits easy removal of the space discharge devices and affords very complete screening between the input and output circuits of each device. v

The embodiments of the invention illustrated and described herein have been selected for the purpose of clearly setting forth the principles involved. It will be apparent, however, that the invention is susceptible of being modified to meet the different conditions encountered in its use and I therefore aim to cover by the appended claims all modifications within the true spirit and scope of my invention.

- vacuum tube extending nection with said conductive screen and for a terminal of each of said condensers.

2. The combination of a space discharge device provided with input and out at circuits and with a screen grid arran to neutralize the capacity coupling between its anode and control grid, current supply means, filter means including impedances connected between said supply means and the anode and screen grid of said device and a plurality of filter condensers associated therewith, a conductive screen interposed between said circuits, and a conductor connected with a terminal of each of said condensers and having a single terminal connection with the screen.

3. The combination of a conductive screen including a pluralit of separate compartments, and a plura 'ty of space discharge devices each arranged to extend from one to another of said compartments and provided with input and output circuits enclosed in different compartments.

4. The combination of a screen including a plurality of sloping partitions, and a plurality of space discharge devices each arranged to extend through a difi'erent one of said partitions and provided with input and output circuits located on difierent sides of the partition through which it extends.

5. A vacuum tube extending through .a metallic shield plate and having an input circuit located wholly on one side of said plate, and an output circuit located wholly on the opposite side of said plate, and means for reducing the inherent capacity between the tube elements.

6. In a multistage vacuum tube amplifier, each stage of which includes an input circuit and an output circuit, a plurality of shielded compartments, certain of which enclose the output circuit of one stage and the input circuit of the succeeding stage, the input circuit of the first of which stages and the output circuit of the second of which stages are each enclosed in other shielded compartments, each partly into each of two of the compartments. I In witness whereof, I have hereunto set my hand this 5th day of February, 1927.

ALBERT W. HULL.

' What I claim as new and desire to secure by Letters Patentof the United States, is:

'1. The combination of a space discharge device provided with input and output circuits and with a screen grid arranged to neutralize the capacity coupling between its anode and control grid, current supply means, filter means including a plurality of filter condensers connected to said device between said device and said supply means, a conductive screen interposed between said circuits, 

